Regulation of oocyte number during oocyte differentiation in the lizard Podarcis sicula

Glyphosate Interference in Follicular Organization in the Wall Lizard Podarcis siculus

Glyphosate (Gly) is a broad-spectrum herbicide widely used thanks to its high efficiency and low toxicity. However, evidence exists of its toxic effects on non-target organisms. Among these, the animals inhabiting agricultural fields are particularly threatened. Recent studies demonstrated that exposure to Gly markedly affected the morphophysiology of the liver and testis of the Italian field lizard Podarcis siculus. The present study aimed to investigate the effects of the herbicide on the female reproductive system of this lizard in order to have a full picture of Gly-induced reproductive impairment. The animals were exposed to 0.05 and 0.5 μg/kg of pure Gly by gavage for 3 weeks. The results demonstrated that Gly, at both doses tested, profoundly interfered with ovarian function. It induced germ cells' recruitment and altered follicular anatomy by anticipating apoptotic regression of the pyriform cells. It also induced thecal fibrosis and affected oocyte cytoplasm and zona pellucida organizations. At the functional levels, Gly stimulated the synthesis of estrogen receptors, suggesting a serious endocrine-disrupting effect. Overall, the follicular alterations, combined with those found at the level of the seminiferous tubules in males, suggest serious damage to the reproductive fitness of these non-target organisms, which over time could lead to a decline in survival.

Spring and Fall recrudescence in Podarcis siculus ovaries: A role for progesterone

In the lacertid Podarcis siculus the reproductive cycle is typically biphasic, with alternate recrudescence (Spring and Fall) and resting (Summer and Winter) phases. This study aimed to shed some light on the role exerted by progesterone during the two recrudescence periods; to this purpose, exogenous progesterone was administered intraperitoneally and the effects on oogonial proliferation, oocyte recruitment, and follicle cells apoptosis were determined. The presence and distribution of progesterone receptors was also investigated by immunohistochemistry and western blotting. Results indicate that progesterone would play different roles and follow different route of action in the two recrudescence periods thus confirming the complexity of the mechanisms controlling oogenesis in this species of vertebrate.

Cadmium impairment of reproduction in the female wall lizard Podarcis sicula

The exposure to environmental toxicants such cadmium (Cd) is an important research area in wildlife protection. In this study, the effect of Cd oral administration on the ovarian structure and function and on reproductive performance of the Italian wall lizard Podarcis sicula was studied. In vivo, adult female lizards were randomly assigned to three groups. Cd was given with food in single dose and in multiple doses 3 days/week for 4 weeks at dose of 1.0 μg/g body weight. Following euthanasia, the ovaries were removed and analyzed for morpho-functional changes. Results demonstrated that Cd increases prefollicular germ cells number; the evaluation of the number of follicles detects significantly higher number of atretic growing follicles, whereas primary follicles remain unchanged with respect to controls. After Cd treatments, follicles are deformed by the presence of large protrusions and a general dysregulation in the follicle organization is observed. The zona pellucida is also affected. Cd causes alteration in sugar metabolism and in metallothionein gene expression. Finally, Cd administration significantly reduces clutch size and dramatically increases embryo mortality. In conclusion, data here described show that Cd induces morpho-functional alterations in lizard follicles and indicates that these are responsible for a significant impairment of oogenesis. The effects of the dose are time independent, persisting essentially unchanged regardless of single or multiple administration, so it can be concluded that even occasional, sublethal Cd contamination may significantly impair reproductive performance in these animals.

The maturation of oocyte follicular epithelium of Podarcis s. sicula is promoted by D-aspartic acid

We investigated whether the maturation of oocyte follicular epithelium of lizard is affected by d-aspartic acid (d-Asp). Our results demonstrated that d-Asp is endogenously present in the oocytes, and its distribution varies during the reproductive cycle and following intraperitoneal administration. At previtellogenesis, it is observed in the cytoplasm and nucleus of pyriform cells, in intermediate cells, in some small cells of the granulosa, in the ooplasm, and in some thecal elements. At vitellogenesis, d-Asp is localized in the proximity of the zona pellucida, in the theca, and in the ooplasm. Injected d-Asp is mainly captured by pyriform cells and ooplasm of previtellogenic oocytes, but a moderate accumulation is evident in the cytoplasm of some small granulosa cells and in the theca. d-Asp also increases the ovarian and plasmatic levels of 17β-estradiol and decreases those of testosterone. As a direct and/or indirect consequence of d-Asp, previtellogenic oocytes grow up and mature, resulting in a higher accumulation of carbohydrates in the granulosa, zona pellucida, and ooplasm, but also a reduction in the thickness of the granulosa layer and an increase of the theca stratum. Taken together, our results show that d-Asp may be related to the synchrony of reproduction, either enhancing the growth and maturation of follicular epithelium or influencing its endocrine functions.

Localization of c-kit and stem cell factor (SCF) in ovarian follicular epithelium of a lizard, Podarcis s. sicula

We performed an immunohistochemical study to determine the immunolocalization of c-kit and stem cell factor (SCF) in ovarian follicles during the reproductive cycle of the lizard, Podarcis s. sicula. Follicles were serially cut and used for histological and histochemical characterization and also for immunohistochemical detection of both c-kit and SCF. C-kit and SCF were localized in the follicles with a differing pattern with regard to the stage of sexual cycle or the cell type forming the follicular epithelium (granulosa). In pre-reproductive follicles, where the granulosa consists of three main different cytotypes, the c-kit receptor was prevalently localized on the plasmalemma of small cells, although some pyriform and intermediate cells also appeared positive. C-kit was also localized in the theca. In pre-reproductive follicles, SCF was markedly observed in the cytoplasm of some pyriform cells. Small cells and theca also stained moderately positive, whereas the intermediate cells were mostly negative. In reproductive follicles, where granulosa cells are morphologically rearranged, c-kit was observed in small cells and in some thecal elements, while SCF was weakly immunostained. At the site of follicular layer invaginations evident c-kit/SCF immunostaining was observed in the granulosa epithelium and in the theca. These observations suggest that the expression of c-kit and SCF changes as a function of follicular development and may reflect the involvement of this system in the maturation of the oocyte.

Ovarian histology of the placentotrophicMabuya mabouya(Squamata, Scincidae)

Ovarian structure and folliculogenesis of females at different reproductive stages are described for the viviparous placentotrophic lizard Mabuya mabouya. The small ovaries have a thin wall formed by the ovarian epithelium and a thin tunica albuginea. One to two germinal beds that contain numerous oogonia and developing primordial follicles are derived from the ovarian epithelium and are next to the ovarian hilum. The ovarian cortex contains follicles at different stages of development, corpora lutea, and atretic follicles. The yolk nucleus and Balbiani complex were not evident in the ooplasm of previtellogenic follicles. The follicular epithelium of these follicles is polymorphic, as in other species of Squamata, but the larger cells are spherical and monolayered rather than pyriform. The zona radiata of the preovulatory follicles is less developed than in lecithotrophic species. These features suggest a decrease in metabolic and absorptive processes during follicular growth. In preovulatory follicles (1.5-1.8 mm diameter), primordial yolk vacuoles and small cortical granules are deposited in the ooplasm instead of fatty yolk platelets, so that only one stage of vitellogenesis is observed. Polyovular atretic follicles occur in some females. Follicular atresia is minimal for preovulatory follicles, but is more frequent in follicles with polymorphic epithelia. In the corpus luteum, the luteal tissue is formed from granulosa cells and luteolysis occurs during the late gastrula -- late neurula embryonic stages. Thus, the maintenance of gestation from the pharyngula to preparturition stages seems to be related to secretion of extraluteal progesterone, possibly of placental origin. These observed ovarian features are related to the high degree of placental complexity of this species and show that the evolution of advanced placentotrophy in species of this lineage has been accompanied by concomitant changes in ovarian function.

Storage in the yolk platelets of low MW DNA produced by the regressing follicle cells

The present work was carried out to clarify the nature and origin of the yolk DNA present in vitellogenic oocytes of the lizard Podarcis sicula. Morphological and biochemical evidences indicate that it has an intrafollicular origin, from the apoptotic bodies resulting from follicle cells regression at the end of previtellogenesis. This conclusion is reinforced by the observation that the oocyte membrane, in in vitro experiments, is unpermeable to exogenous DNA. Biochemical evidences reveal that the yolk DNA has a low (200bp) molecular weight and this suggests that it is produced by the endonucleases typically involved in apoptotic DNA laddering. Indeed, immunocytochemical analyses demonstrate that follicle cells contain significant amounts of DNAse I. In immunoblots, carried out during different periods of the ovarian cycle, the enzyme shows a MW of about 33, 66 or 100 kDa thus indicating that its activity in the follicle of Podarcis is modulated by dimerization and/or binding to regulatory factors. Mol. Reprod. Dev. 59: 422-430, 2001.

Pyriform cell differentiation in Podarcis sicula is accompanied by the appearance of surface glycoproteins bearing alpha-galNAc terminated chains

The present histochemical and cytochemical study using a lectin panel (WGA, GSI-A4, GSI-B4, PSA UEA-I, PNA, LCA, Con-A, DBA, MPA, BPA) has demonstrated that, in Podarcis sicula, the differentiation of small follicle cells into pyriform cells by means of intermediate cells is accompanied by the appearance of glycoproteins bearing alpha-GalNAc terminated O-linked side chains on the cell surface. The distribution of DBA- and MPA-binding sites over the follicular epithelium changed during the different stages of oocyte growth. DBA- and MPA-binding sites first appeared at the beginning of folliculogenesis within the zona pellucida (ZP) and on the surface of small cells, i.e., the stem cells of pyriform cells. Afterward, labeling was evident on the cell surfaces of intermediate cells and, later on, also of pyriform cells. On the other hand, no labeling was detected on the small cells located under the basal lamina, which, reportedly, do not differentiate into pyriform cells (Filosa et al. J. Embryol. Exp. Morphol., 1979; 15:297-316). Once pyriform cells were differentiated, the distribution of DBA- and MPA-binding sites over the follicular epithelium remained unchanged until intermediate and pyriform cells underwent apoptosis (Motta et al. J. Exp. Zool., 1996; 276:233-241) and the follicular epithelium transformed into a monolayer composed of small follicle cells only (Filosa Mon. Zool. Ital., 1973; 7:151-165). During this stage of oocyte growth, DBA and MPA labeling gradually decreased to completely disappear in the follicular epithelium of vitellogenic follicles. It is noteworthy that the observed changes in the distribution of DBA- and MPA-binding sites represent the first evidence recognized by lectins of a gradual modification of surface glycoprotein distribution over the follicular epithelium in the ovarian follicles of nonmammalian vertebrates so far studied. Finally, the zona pellucida (ZP), characterized by the presence of GalNAc, GluNAc, Man, and Gal, was demonstrated to be first synthetized by the oocyte and later on by the follicle cells.

Control of oocyte recruitment: regulative role of follicle cells through the release of a diffusible factor

To determine whether oogonial proliferation and oocyte recruitment are under control of hypophyseal and/or ovarian factors, we carried out a series of investigations using Podarcis sicula, a lizard inhabiting the temperate lowlands of Europe in which oocyte recruitment occurs throughout the year, as animal model. Germinal beds containing oogonia and oocytes in prefollicular stages were cocultured with different ovarian compartments in presence/absence of FSH, and the effects of different treatments were evaluated by counting the number of prelepto-leptotene oocytes. Results revealed that oocyte recruitment from the pool of oogonia is under the control of a factor released by follicle cells while FSH has an indirect effect on modulating oogonial proliferation. SDS-PAGE analyses carried out on media conditioned by follicles suggest that the factor involved in the control of oocyte recruitment may be a small protein (about 21 kDa) and that its release is dependent on the period of the ovarian cycle but apparently not on the circulating levels of FSH.

Ribosomal gene amplification in oocytes of the lizard Podarcis sicula

In order to provide cytological evidence of amplification, Podarcis sicula oocytes were studied by cytophotometry, thymidine incorporation and in situ DNA-DNA hybridization. Our results show that DNA replication is completed during the preleptotene stage, the leptotene oocytes having the typical 4C nuclear DNA content. Between the zygotene and the mid-pachytene stages further DNA synthesis occurs with consequent increase of the ribosomal nuclear DNA content. These results and the variations in nucleolar organization observed during differentiation give clear evidence of the existence of ribosomal gene amplification in Podarcis sicula oocytes.